Elucidation of Structure and Dynamics in Solid Octafluoronaphthalene from Combined NMR, Diffraction, And Molecular Dynamics Studies

Abstract

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Well-Tempered Metadynamics as a Tool for Characterizing Multi-Component, Crystalline Molecular Machines

“…In our previous studies of this material we showed that even 100 ns long molecular dynamics simulations are insufficient to sample the full rotation of the molecules, a process shown to occur by solid-state NMR. 32 Our first goal here is to show that the use of metadynamics can make the sampling of this rotation facile, confirming both the effectiveness of the method and further validating the NMR results in that study. Secondly, we extend the method to sample from the simultaneous rotational behavior of three neighboring OFN molecules, proving that they are correlated and investigating the mechanism behind the effect.…”

“…We have shown previously using unbiased MD simulations that the movement of OFN molecules is governed principally by their in-plane rotation, 32 the definition of which is described above.…”

“…Details of how this cell was constructed from the disordered crystal structure are given in the original reference, 32 along with the full simulation details for the 100 ns run. The modified OPLS charges and van der Waals parameters detailed in that work were also used here.…”

“…32 This correlation would manifest itself in small modifications to the effective rotational FES of each individual molecule as the orientations of its neighbors change. Reliably estimating such small changes requires a very high level of sampling that would be unfeasible to achieve using unbiased MD simulations.…”

NMR characterisation of dynamics in solvates and desolvates of formoterol fumarate

“…While a variety of NMR parameters are sensitive to dynamics on different timescales, it is often difficult to interpret the results obtained in terms of specific motions. Although molecular dynamics simulations are increasingly used to link NMR observations in molecular solids to molecular-level processes [38], such modelling requires an initial structural model. Interpretation of parameters such as NMR relaxation times is especially difficult in the context of heterogeneous and disordered systems, since the dynamic processes are unlikely to be well defined.…”